Nevirapine rather than efavirenz-based HIV treatment more likely to suppress viral load to zero

The inclusion of nevirapine rather than efavirenz in an HIV treatment combination was more likely to suppress viral load in the blood to completely undetectable levels, French investigators report in the online edition of AIDS.

A total of 81% of patients taking nevirapine (Viramune) had a viral load below one copy/ml, compared to 55% of individuals treated with efavirenz (Sustiva or Stocrin). The study involved 165 patients and was retrospective. All the patients had had an undetectable viral load for at least six months and were taking either nevirapine or efavirenz in combination with FTC (emtricitabine, Emtriva) and tenofovir (Viread; the two drugs are usually combined in a single pill, Truvada, and are also available co-formulated with efavirenz in Atripla).

A viral load below 50 copies/ml is the current aim of antiretroviral therapy. Viral load tests in routine use cannot detect virus below this level. However, research assays are able to detect extremely low levels of residual viral load.

Previous research has suggested that therapy that includes a non-nucleoside reverse transcriptase inhibitor (NNRTI) is more likely to suppress viral load to extremely low levels than treatment based on a protease inhibitor. There is also some evidence that nevirapine is more effective at reducing viral load to the lowest levels than efavirenz.

French investigators wanted to gain a better understanding of the impact of nevirapine- or efavirenz-containing regimens on residual viraemia. They therefore designed a retrospective study involving 75 patients treated with nevirapine and 90 individuals taking efavirenz-based therapy.

To be included in the study, patients were required to have had a viral load below 50 copies/ml for at least six months.

Viral load was monitored using an assay capable of detecting virus below one copy/ml.

Overall, 81% of patients taking nevirapine had a viral load of zero compared to 56% of individuals treated with efavirenz.

After controlling for potentially confounding factors, the investigators found that treatment with nevirapine was significantly more likely to suppress viral load below one copy/ml than therapy with efavirenz (odds ratio [OR]: 2.85; 95% CI, 1.4 to 6.1, p  = 0.005). The only other factor associated with a viral load of zero was the duration of viral load suppression below 50 copies/ml (OR: 2.07; 95% CI, 1.3 to 3.5, p  = 0.005).

The investigators believe that research now shows “the stronger ability of nevirapine than efavirenz to better control residual viremia, in patients presenting with low viremia.” They suggest that this is because nevirapine is better able to penetrate into anatomical sites that may harbour “reservoirs” of virus.

“The clinical relevance of having a viral load below 1 copy/ml has yet to be shown,” conclude the researchers, who call for studies “to explore, for example, the relationship between the level of residual viremia and systemic inflammatory or immune activation markers.”